This invention relates to a process for the removal of ink from printed wastepaper in the course of reclaiming the fiber content of the waste for reuse in the manufacture of new paper. More particularly, the invention relates to a process for the deinking of xerographically printed paper.
Wastepaper has long served as a source of the raw fiber materials used in papermaking. Traditionally, fiber from wastepaper was utilized only in the production of low grade paper and paperboard products. Today, however, greater utilization of reclaimed fiber (about 25 percent of the total fiber used in papermaking) has provided incentive for taking steps to upgrade the reclaimed product. These steps include treatment to effectively remove ink from waste fibers in order to permit their use in the manufacture of high quality papers.
In the course of the conventional paper reclamation process of interest, deinking procedures include steps for converting the wastepaper to pulp and contacting the pulp with a alkaline aqueous deinking medium containing a chemical deinking agent. The physical pulping and the alkalinity of the aqueous medium cause the removal of ink from the pulp fiber and the deinking agent produces a suspension, (and/or dispersion) of the ink particles thus removed into the aqueous medium. The resulting mixture is subsequently treated to separate the suspended ink from the pulp.
A variety of materials, particularly surfactants and mixtures of surfactants are known to be useful as deinking agents in such a process, at least when the process is applied to the deinking of such common wastepaper stocks as newsprint, book, magazine, and ledger. It is recognized, however, that conventional processes have not been particularly successful in specific application to xerographically printed wastepapers. The difficulty encountered in the deinking of xerographics has been attributed to the character of the xerographic ink, specifically the binder, which is fundamentally different from that used in other printing processes. For example, in distinction to the common oil or resin binders of other inks, the xerographic ink binder is typically a polymeric material (e.g. polyethylene) which during the printing process is fixed to the paper by the application of heat.
The ever-increasing utilization of xerographic printing has made the reclamation of xerographic waste economically attractive. Accordingly, the object of the present invention is a deinking process which is effective in the treatment of xerographic waste stock.
With specific regard to certain nonionic surfactants which are useful in the process of the present invention, it has been established (U.S. Pat. No. 4,162,186) that they may have advantage in general deinking service from the standpoint of both performance in ink removal and also biodegradability in process effluents. It has been found, however, that neither such a nonionic surfactant used individually nor a combination of two nonionic surfactants as described by the aforementioned patent is effective as a deinking agent in application to xerographically printed waste.